1. Field of the Invention
The present invention relates to a method for fabricating a plate-type magnetic resistance (hereinafter referred to as xe2x80x9cMRxe2x80x9d) sensor chip element, which is used for controlling rotational speeds of capstan motors for use in VCR, camcoders, and the like. More particularly, the present invention relates to the use of a glass wafer in fabricating a plate-type MR sensor chip simply and easily.
2. Description of the Prior Art
In order to better understand the background of the invention, a description will be given of a fabrication method of a conventional MR sensor chip in conjunction with FIG. 1. For the fabrication of a conventional MR sensor chip, to begin with, sensing parts 21, serving as characteristic membrane detectors, are formed on a ceramic glass sheet 11 while terminal parts are patterned on one end of the ceramic glass sheet 11, as illustrated in FIG. 1. The resulting structure is diced into individual rectangular MR sensor chips 20.
Each rectangular MR sensor chip is bonded onto a chip holder 30 made of an insert injection via an adhesive. A lead frame 30 is connected to the terminal part 22 of the MR sensor chip 20 by soldering, followed by coating an epoxy resin 50 over the terminal part to protectively insulate the solder connection between the lead frame 30 and the terminal part 22.
The conventional MR sensor chip 20 fabricated as in above is mounted at one side of a magnet 70 on a motor board 60 in such a way that the MR sensor chip 20 stands facing the magnet to control the rotational speed of the magnet 70, as shown in FIG. 1.
As disclosed in the above description, the fabrication of the conventional MR sensor chip requires complex processes, including insert injection for molding the chip holder 10 for fixing the MR sensor chip 20, soldering for connecting the lead frame 30 to the terminal part of the MR sensor chip 20, and application of the epoxy resin 50 to insulate the soldering portion.
Particularly, the ceramic glass sheet 11 of the MR sensor chip 20 is expensive and thus imposes an economic burden on both manufacturers and consumers. Both the sensing part 21 and the terminal part 22 are integrally formed onto the ceramic glass sheet 11. However, since the terminal part 22 protrudes from the surface of the ceramic glass sheet 11, insulating epoxy resin 50 is required to be applied on the soldering 40, but this treatment makes the terminal part 22 more prominent. When the MR sensor chip 20 fixed to the chip holder 10 is mounted onto the motor board 60, there occurs interference between the magnet, serving as a rotor, and the projection of the epoxy resin coated on the terminal part 22.
A solution to this problem is the use of processed ceramic wafers or photosensitive glass which allows the terminal part to be formed on the back side. However, this solution is economically unfavorable because the substrates are very expensive and the fabricating process is complicated.
Therefore, it is an object of the present invention to overcome the above problems encountered in prior arts and to provide a method for fabricating an MR sensor chip easily and simply.
It is another object of the present invention to provide a method for fabricating a plate type MR sensor chip which is structured to have a terminal part on both sides thereof and thus can be mounted onto a board of a magnet without the aid of a separate holder.
Based on the present invention, the above objects could be accomplished by a provision of a method for fabricating a plate type magnetic resistance sensor chip, comprising the steps of: establishing sensing parts by depositing a characteristic membrane composed of NiCo and NiFe at 200 to 500xc2x0 C. to a thickness less than 1,000 xc3x85(Angstrom) on a surface of a glass wafer, exposing the membrane to light, and etching the membrane in a predetermined pattern; forming a protective film atop each of the sensing parts by depositing a SiO2 membrane to a thickness of 0.2 to 0.7 xcexcm over the glass wafer, exposing the SiO2 membrane to light, and etching the SiO2 membrane in the same pattern as in the sensing part; subjecting the resulting structure to sand blasting to form through-holes at every corner of the sensing parts; depositing a NiFe film around the through-holes on both sides of the glass wafer and within the through-holes; and dicing the glass wafer into individual rectangular magnetic resistance sensor chips in such a way that each magnetic resistance sensor chip has four arc corners with a NiFe conductor established at every arch corner on both sides of the wafer glass, said NiFe conductor serving as a terminal part.